The remarkable chemical and physical properties of diamond films make them excellent materials for a broad range of scientific and industrial applications. A number of chemical vapor deposition (CVD) techniques have been proposed and have proven to be feasible for growing polycrystalline diamond films from mixtures of methane or other carbon-containing gases with hydrogen or oxygen. In accordance with these techniques, the reactive species are produced by decomposing the gas mixtures either thermally by means of hot filaments or kinetically using hot electrons in a cold plasma or both electrons and ions in a thermal plasma. For example, an article by Singh, Mesker, Levine, and Arie, Hollow Cathode Plasma Assisted Chemical Vapor Deposition of Diamond. 52 Applied Physics Letters 1658 (May 16, 1988), incorporated herein by reference, discloses a diamond deposition method utilizing a hot hollow cathode which combines both thermal and plasma dissociation of reactant gases. Neither this nor any other existing technique, however, combines the thermal and kinetic processes to produce large area electron beams and plasmas and achieve uniform deposition of diamond films.
In addition, other hollow cathodes have been designed, including a 6 mm diameter open tantalum tube and a 6 mm diameter molybdenum tube having a 3 mm diameter thermally-isolated tantalum insert and a 1 mm diameter aperature. These tubes lack low impedence plasma characteristics, however, and therefore require relatively high voltages for ignition and operation at a specified current. These prior designs also cannot be scaled readily to achieve large area electron beams and plasmas.